Architect Mike Davies doesn't just dress in red - he drives a red Jaguar with red leather seats, writes in red ink with a red pen and studies the stars from his roof through 22 red telescopes. "Colour is a vehicle to exploring life," says Davies, a founding partner of Richard Rogers Partnership. "The range inherent in a colour is so incredible." In his spare time he paints "symphonies in red", and he still adheres to an idealism of art that many left behind at college.

He had been doodling the Millennium Dome in red - a sketch similar to the one with which he started the £758m project in 1996. It was, he says, "a simple, honest, elegant and minimalist answer to a very big, simple problem".

With the day of judgment on his brainchild fast approaching, is he feeling the pressure? Not at all: "Having a deadline that can't be moved is fantastic. There is a palpable atmosphere that we are on a ship in the middle of the Atlantic and none of us can jump off. Everyone is committed to making it a success."

If this upbeat attitude sounds improbable, Ove Arup & Partners director Chris Wise, who has worked with Davies for more than 11 years, says it rings true to his character. "He is a real enthusiast and a dreamer," says Wise. "Maybe that's what enables him to do difficult projects like the dome. He'll take the bad and the good and do the best he can in situations which someone else would run away from."

This charm and enthusiasm overwhelms one's initial response to the garish attire. Wise says he was horrified when he first set eyes on him, but after a couple of hours it was apparent that Davies had the strength of character to carry it off.

Despite sometimes vitriolic media scrutiny, Davies says he has no qualms about the cost of the dome, and few about its design. "We are only the cover - which is £42m, or 7% of the total project cost."

He did not set out to create a great monument, but rather a natural public gathering place. "The dome should not be over-read. In fact, it is not an architecture project at all. It is a lightweight, loose-fit, friendly cover. It is the lightest large-scale structure on the planet. And it's festive. It is no accident it does this," he says, showing how the dome's yellow masts resemble outstretched arms in his doodle.

If Davies weathers controversy well, it maybe because he is no stranger to it. His other current project - the £8bn Heathrow Terminal Five for BAA, four times bigger than the dome and perhaps even more controversial - has been mired in a public inquiry since 1995. Davies expects to be the terminal's project director after the dome opens. Although the project has been dogged by delays, changes in the brief and cost-cutting drives, he is optimistic about its future: "Further expansion is inevitable - it just has to be done responsibly."

Has he ever hankered after his own practice? "No, because I'm a team player. We are an amazing problem-solving team. I have worked with seven of the guys for 27 years, so there is a certain commonality of feel to us that has been useful. The shorthand between us is very good. We have a lot of skill and experience from having done odd projects like Pompidou, Lloyd's, Channel 4, the dome. Compared with run-of-the-mill buildings, you learn so much."

He says the concept of a signature architect is an anachronism. "The days of Norman [Foster] have gone, the days of Richard have gone," he says. "The days of multidisciplinary top-end practices are here." As Davies is a man who has never lost the ideals of flower power, you tend to believe this non-egotistical stance.

Born in Wales, Davies lived in Egypt and Cyprus as a child and travelled with his geographer father to 18 countries before his 18th birthday. "It gave me a wonderful architectural education," he says. "I got to stand inside the Great Pyramid of Giza when I was 11 - although it was standing beside the Skylon at the 1951 Festival of Britain when I was nine that made me want to be an architect." He studied at the Architecture Association with two of the other Richard Rogers founders, Marco Goldschmied and John Young. In those days, Davies wore electric purple. He went on to do an MA at UCLA and stayed in California to co-found a multidisciplinary practice, Chrysalis, which did 52 projects in three years, including the Pepsi Cola pavilion at the Osaka Expo in 1970. He joined Renzo Piano and Rogers shortly after the practice won the contract for the Pompidou Centre in 1971. It was while working on it that he switched from wearing purple to red: "I used to get my bottom pinched on the Paris metro. It was the code colour for the Parisian gay community," he explains, "so I thought it was time to change. I thought, what's another wonderfully rich, cheerful colour to explore?"

Sartorial idiosyncrasies aside, what distinguishes Davies from his partners? Rogers is the public, and increasingly political, face of the practice; Goldschmied is seen as the business brain; Young is credited with the design strength. What is Davies's forte?

"I enjoy all aspects of the process," he says, "but I particularly enjoy starting the concept design, because I think it's the most difficult and interesting thing to do. We have this 95% adage. Getting the concept right at the beginning is 80% of the battle. During the course of the design development, construction and evolution of the client's brief, you can regain another 15%. You never get the last five. That's why we continuously tune if we can."

In architectural circles, Davies is known as a technological evangelist with a keen interest in research and development, particularly in glass technology. He pioneered the concept of intelligent building skins in the 80s as part of a research project with Pilkington.

He is also credited with developing the practice's urban design and masterplanning expertise - he was in charge of the Royal Docks and Greenwich Peninsula masterplans. He says masterplanning inspires him: "If you can create a vision that enough people will subscribe to and support that it becomes the way forward, that is a powerful weapon."

The practice's policy of keeping staff numbers down is critical to its design approach. "We try to stay this size so that we can all remember and communicate with each other and all fit into one room. We have a directors' design meeting on a Monday that is an open meeting. Anybody can come in. If the office junior wants to come in and say, 'It's a load of bullshit', they can. There is no status to it. Whoever carries the intellectual argument wins the day."

This egalitarianism has been noted by Wise. "He is not a snob. He will chat to anyone about anything. Maybe that's why he's into climbing. Whoever you are climbing with, all that matters is getting from the bottom to the top." When Davies is not climbing at Harrison Rock in Tonbridge, he is sailing his yacht out of Poole harbour. "You need to get out on the ocean to maintain your equilibrium," he says. "You can't keep this up 365 days a year."

So the pressure does get to him? "As a practice, we are very aware that for the first three years it was called Richard Rogers's Millennium Dome. We know that, even though we are a small part of it, if it doesn't take off, it will be 'Richard Rogers's dome failure', " he concedes.

Whatever happens, Davies will face the music, celebrating new year's eve 1999 with Tony Blair and assembled dignitaries in the dome. Might the dawn of a new century precipitate another colour switch? "You never can tell. I know the next colour I would investigate would be yellow - but it might take a while to make the change and I might be dead before it happens. But I think it's very interesting, yellow. Very interesting."